1. Field of the Invention
The present invention relates to a power transmission system of a hybrid electric vehicle. More particularly, the present invention relates to a power transmission system of a hybrid electric vehicle which minimizes power delivery loss and improves fuel economy by optimizing operation point of an engine.
2. Description of Related Art
Environmentally-friendly technique of vehicles is very important technique on which survival of future motor industry is dependent. Vehicle makers are focusing on development of environmentally-friendly vehicles to meet environment and fuel consumption regulations.
An electric vehicle (EV) and a fuel cell electric vehicle (FCEV) that are zero emission vehicles (ZEV) are developing as environmentally-friendly vehicles.
The electric vehicle and the fuel cell electric vehicle have merits of no emission, but have limitations, that is technical problems such as battery capacity, battery life, and so on, and construction of infrastructure such as charging stations.
Therefore, a hybrid electric vehicle using a conventional internal combustion engine and an electric motor has been developed and commercialized.
The hybrid electric vehicle is a vehicle driven by combination of electric power and power of the internal combustion engine. A typical hybrid electric vehicle uses a motor and a gasoline engine, and has high efficiency and can reduce exhaust gas efficiently by controlling power sources to be operated at a high-efficiency point of a system.
In addition, the hybrid electric vehicle does not demand additional charging stations but improves fuel economy and secures similar travel distance to a gasoline vehicle. Therefore, the hybrid electric vehicle will be mainly used as future environmentally-friendly vehicles.
Meanwhile, power flow of the hybrid electric vehicle includes mechanical power flow where power of the engine is directly transmitted to an output shaft using power split device such as planetary gear sets that distribute flow of power, and electric power flow where a generator generates electricity using the power of the engine and a battery is charged by the generated electricity or a motor is driven by energy of the charged battery.
A hybrid system of power split type can operate the engine independently from the output shaft, can turn on or off the engine freely during running, and can achieve an electric vehicle mode.
In addition, since the hybrid system can achieve an electrically variable transmission (EVT) using two motor/generators, the engine may be operated efficiently.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.